In the field of automotive vehicles, active sensors are used for recognizing rotational speeds and for picking up the signal of a rotating magnetic encoder through a sensor element. The magnetic oscillations of the magnetic field caused by the encoder are detected by the sensor element, amplified and converted into two current levels by a processing unit. The frequency of the signal produced in this way is proportional to the rotational speed of the encoder.
The rotational speed active sensors currently used in the field of automotive passenger vehicles comprise a free data bit in the sensor log that can be used for transmitting further measured data. From DE 196 50 935 A1 it is known, for instance, to transmit through a common signal line, the data of a rotational speed sensor as well as additional data of further sensors, for example, data on the brake lining wear, on the interferric gap between the encoder and the sensor element, on the temperature at the wheel, on the deflection path of the oscillation dampers etc. through a common signal line. The data of the rotational speed sensor exist in the form of an alternating signal. A sequence of sensor pulses of a defined duration is gained from this alternating signal, the information on the rotational speed being contained in the pulse pauses. The additional data are also transmitted in the pulse pauses. A separation of the rotational speed sensor data and the additional data is assured through different signal levels or current amplitudes. If it is required to transmit the logic state 1 for a bit of the additional data, a current pulse is created during the time span reserved for this bit at a current level situated between a basic level (corresponding to the logic state 0) and the current level of the sensor pulse of the rotational speed sensor.